The present invention relates to a liquid crystal display apparatus, particularly to a TFT active matrix type liquid crystal display apparatus capable of low power consumption.
A conventional driving system of a TFT active matrix type liquid crystal display apparatus will be explained hereinafter. A known active matrix type panel technique is described in detail in Shunsuke Kobayashi "A Color Liquid Crystal Display" Sangyo Tosho Co. Ltd.
The TFT active matrix type liquid crystal display apparatus is driven by using a line-at-a-time scanning method, in which one scanning pulse is applied every one frame period of time. One frame period is generally set to about 1/60 second. These pulses applied from the top panel to the bottom panel each has a certain delay of time in the order from top to bottom.
Because one pixel is formed of 3 dots in a color panel having 640.times.480 dots, the total number of dots is 1920.times.480. Further, because 480 gate wires are scanned in one frame, the time width of the scanning pulse is about 37 .mu.s.
Liquid crystal driving voltages, to be applied to the liquid crystal to which the scanning pulse is applied, are applied to signal electrodes in synchronization with the scanning pulse. In the selected pixel to which the gate pulse is applied, the voltage of a gate electrode of the TFT connected to the scanning electrode increases, and thus the TFT turns to the "ON" state. At this time, the liquid crystal driving voltage is applied to a display electrode via a source and a drain of the TFT, and thereby the pixel capacity is charged, being comprised of the liquid crystal capacity formed between the display electrode and an opposed electrode formed on an counter substrate and a load capacity provided to a pixel. By repeating this operation, the liquid crystal applying voltage is applied repeatedly to the pixel capacity of the whole surface of the panel every frame time.
Further, because an alternating voltage is required to drive the liquid crystal, a voltage whose polarity is inverted every frame time is applied to the signal electrode. Therefore, the liquid crystal driving frequency is 30 Hz, a half of the normal frame frequency of 60 Hz. As a result, flicker appears and it becomes difficult to watch the display. In the conventional liquid crystal display apparatus, the effect of such flicker is decreased by inverting alternately the polarity of the liquid crystal driving voltage at every adjacent pixel. Most of the electric power for driving the liquid crystal panel is consumed in the repeated charging and discharging of the capacity at intersecting portions of the scanning wires and the signal wires and the capacity of the liquid crystal between the wires and the opposed electrodes formed on the whole surface of the counter substrate every time the gates are selected.
In the current panel configuration and the liquid crystal driving system, the electric power consumed to repeatedly charge and discharge the capacity at intersecting portions of the scanning wires and the signal wires and the capacity of the liquid crystal between the wires and the opposed electrodes formed on the whole surface of the counter substrate every time of the selection of the gates, occupies a major percentage of the total power consumption. While it is possible to reduce the power consumption by narrowing the width of the wires or lowering the liquid crystal driving frequency, to narrow the width of the wires leads to an increase in the high impedance resulting in signal delay and distortion, and to lower the liquid crystal driving frequency leads to a drop in the response speed of the display and the occurrence of flicker.